$ { {5} \times \left[\begin{array}{rr}{3} & {1} \\ {4} & {-2}\end{array}\right] = {?} } $
Solution: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{rr}{5}\times{3} & {5}\times{1} \\ {5}\times{4} & {5}\times{-2}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{15} & {5} \\ {20} & {-10}\end{array}\right]}$